This invention relates to apparatus and method for examining a printed circuit board provided with electronic circuit elements and, more particularly, to those for checking whether a miniaturized electronic element mounted on a circuit board is at a correct position.
Recently, electronic parts in the form of chip elements, such as miniaturized electronic elements, have become popular and are replacing electronic parts with leads. Such chip elements are often mounted on circuit boards together with electronic parts with leads. When assembling such a circuit, chip elements are first temporarily bonded by adhesive to a circuit board at given locations thereof and, after the adhesive is cured in a drying chamber, the chip elements are permanently soldered. Where electronic circuits are produced on a mass production basis, the temporary bonding of chip elements on the circuit board is carried out on an automatic assembly line.
In this case, it is likely that chip elements are mounted in deviated positions or detached from a given position on the circuit board. If such a defectiveness is found after the soldering, the position-correction is very time-consuming, thus increasing the cost of manufacture of the apparatus using the circuit board or reducing the yield. Therefore, it is very important to find out a chip element temporarily bonded in an incorrect position or a missing chip element and take necessary correction measures before regularly soldering the chip elements.
Usually, the checking for chip elements out of right positions and missing chip elements is carried out by visual checking, which requires a great deal of man-hour and is inefficient and poorly reliable.
It has been proposed to check for chip elements out of right positions and missing chip elements by processing image data of the circuit board carrying bonded chip elements that is obtained with an image pick-up camera. In this case, however, if the circuit board that is to be checked is set in an incorrect position or if there is a warp or like deformation of the circuit board itself, accurate position inspection cannot be obtained.